Inroduction to human Body

INTRODUCTION

AN INTRODUCTION TO THE HUMAN BODY

Scientific Name : Homo sapiens  sapiens is scientific name of living modern man. Homo is genus, sapiens and sapiens are species and subspecies respectively. The various racial groups, namely Mongoloid, Negroid, Caucasoid and Australoid are types of this single genus, species, and subspecies.

Man’s  Place in Nature :  Homo sapiens  sapiens belongs to the kingdom Animalia, phylum, Chordata, subphylum Vertebrata,(Craniata), class Mammalia, order Primates, suborder Anthropoidea, family Hominidae.

Apes such as gibbons, orangutans, chimpanzees and gorillas are close to humans.

Origin : The living  modern man evolved about 25,000 years ago from the fossil modern man, Homo sapiens fossilis (Cro-magnon Man). Monkeys, apes and human have common ancestors. Man has not descended from monkeys as some people remark.

Anthropology : Study of origin, physical and mental development, cultural and customs of present and past races of mankind is called anthropology (anthropos=man ; logos=study).

Habitat : Man is terrestrial (lives on land). He has reached all parts of the world and has visited the moon too.

Habits : Man is omnivorus (feeds on both plant and animal foods). He performs true bipedal (on two feet) locomotion. Man has plantingrade gait (walks on soles and heels of the feet). He is normally diurnal (works during the day and rests at night). However, he may become nocturnal by compulsion. Man is social and cultured. He was originally a nomed (wanderer). Man generally believes in God. He worship too. He is monotheist (G. Mono=one, theas=God). Man is generally monogamous (marries a single wife). Some people practices polygamy (have more than one wife ) or (Polygyny) more than one husband (polyandry) at the same time. Humans are viviparous (give birth to young ones). Gestation period 9time between fertilization and birth of the young ones) ia about 9 months. 

Body Division- The Human body is divisible into three division. Head, neck, and trunk. Reappearance of some ancestral, not parental, structures is called atavism. Various human external body parts are briefly described below-

Head- The head has a mouth,chin, nose, eyes, external ears. The upper lip has median notch, the philtrum. The holes of the nose are called nostrils. A small pinkish triangular flap in the inner corner of each eye , called nictitating membrane.

Neck- In mjan the neck has a prominent forword raised portion called adam’s Apple. The neck moves the head.

Trunk- It has two regions upper thorax and lower abdomen.

(I)                            Thorax- It bears a pair of rounded promionences called teats(nipples). Which is functional in women. A pair of shoulders are found.

(II)                         Abdomen- its front side has a prominent pit called the umbilicus(navel). The latter marks the point of attachment of the umbilical cord that connected the foetus to the maternal tissues for nourishment during development.

Phytochrome- The chemical which induces flower formation has been named as florigen. It has not yet been identified. By grafting experiments, it has been found that the stimulus of flowering can pass  from the induced plant to the non induced plant even if the latter is growing under unfavourable photoperiods. The latest thinking about the nature of the chemical stimulus is that , it is a complex of all the  types of growth hormones of their precursors because exogenous supply of one or the other hormone.

Vernalization- Many plants do not come to flower before they experience a low temperature. These plants remains vegetative during the warm season, receive low temperature during winter, grow further and then bear flowers and fruits. It was found by Lysenko (1928) a Russian worker, that the cold requiring biennial plants can be made to flower in one growing season by providing low temperature treatment to young plants or moistened seeds. He called the effect of this chilling treatment as vernalization.

Mechanism- The stimulus recived by the actively dividing cells of shoot or embryo tip traverls to all parts of the plants and prepare it to flopwer. The stimulus has been named as vernalin. It can be passed from one plant to another through grafting in case of Henbane but not in others. Vernalization prepares the plant to flower. The inductions of flowering depends upon the presence of other favourable condition. Photoperiodism, how ever, not only prepares the plant to flower but also brings about flowering.